1. Field of the Invention
The present invention relates to an adhesive composition for hard tissues used in the medical and dental fields, showing strong adhesion to hard tissues such as bone, nail and tooth, and being excellent in peripherical sealability. More specifically, the present invention relates to a dental adhesive composition which is usually used for bonding to a tooth a resin material such as a dental bonding material, a dental luting material, a dental composite resin or a dental compomer, especially for the purpose of giving tooth excellent peripherical sealability in odontotherapy.
2. Discussion of the Related Art
In the restoration of teeth damaged by caries or the like, there have been used a filling restorative material which is a so-called filling composite resin or filling compomer, a crown restorative material such as a dental metal alloy, porcelain or a resin material, and the like. However, since these filling restorative materials and crown restorative materials themselves do not exhibit adhesive properties, conventionally various dental adhesives have been used. Among them, there has been preferably employed a so-called acidic etching-type adhesive system in which a tooth surface is treated with a strong acidic etching agent such as phosphoric acid, and thereafter a bonding material is applied thereto for adhesion.
However, there are some defects in the above method of treating with the acidic etching agent, such that washing with water for sufficiently removing the acid and drying again are necessitated after the treatment. Therefore, there is a defect that its procedures are complicated. According to the adhesive system using an acidic etching agent, adhesive properties for enamel would be improved. However, it is difficult to give dentin high adhesive strength and excellent peripherical sealability.
The term “peripherical sealability” as referred to herein means sealing ability of an adhesive at the bonding portion (peripherical portion). The peripherical sealability can be evaluated by immersing a sample in a solution of a colorant, for instance, an aqueous basic fuchsine solution. When the clearance of the bonding portion between a tooth and an adhesive is large, a large amount of the colorant penetrates into the clearance, so that the adherent is remarkably colored at the peripherical portion. When the adherent is colored as described above, it is thought that the clearance gives one of causations for secondary caries by the invasion of bacteria or foreign substances giving a harmful effect on adhesive properties into the clearance.
As techniques using other adhesives, there have been proposed in Japanese Patent Laid-Open Nos. Sho 62-223289 and Hei 3-240712 an adhesive system in which a tooth is treated with a primer composition composed of an acid or acidic monomer in place of the acidic etching agent, and a hydrophilic monomer, and thereafter a bonding material is applied to the tooth without the procedure of washing with water, i.e. a so-called adhesive system using a self-etching primer. In this adhesive system, adhesive properties and peripherical sealabilities have been improved to some extent especially for dentin.
However, in this adhesive system, the durability cannot be said to be enough even though the self-etching primer is used. Accordingly, there often occurs deterioration in peripherical sealability when the lowering of adhesive strength is small in the durability test of adhesive strength. Therefore, there are often caused some problems in clinics such that leakage is caused between the tooth and the restorative material after the passage of a given time period from restoration, and that caries again progresses from the peripherical portion, thereby generating a so-called secondary caries. Therefore, in recent years, there have been desired further improvements in sealability at the peripherical portion.
An object of the present invention is to provide an adhesive composition for hard tissues, which exhibits excellent adhesive properties for hard tissues, especially tooth such as enamel, dentin or cement, and which is especially excellent in peripherical sealability.
These and other objects of the present invention will be apparent from the following description.